Leverett J-Function
Calculates the Leverett J-function, which normalises capillary pressure by interfacial tension, contact angle and the square root of the permeability-to-porosity ratio. It collapses capillary pressure curves from samples with different properties onto a single rock-type curve. Enter the capillary pressure, interfacial tension, contact angle, permeability in millidarcy and porosity.
Result
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Collapsing capillary pressure curves onto one rock-type
The lab hands back one capillary pressure curve per core plug, and every plug carries its own permeability and porosity. Stacking those curves on a single chart yields a shapeless cloud: the 500 mD sample rises early, the 5 mD sample rises late, and the petrophysicist cannot pull a single saturation function out of it to feed the static model. The J-function exists to strip out what belongs to the sample and keep what belongs to the rock-type.
J = Pc / (σ·cos θ) × √(k/φ), where Pc means capillary pressure in Pa, σ the interfacial tension in N/m, θ the contact angle in degrees, and k the absolute permeability, entered in millidarcy and converted internally to m² through the factor 9.869233×10⁻¹⁶; φ goes in as a fraction. The values already loaded, 35000 Pa, 0.025 N/m, 30°, 120 mD and 0.22, give J = 1.1861. Most of a sandstone saturation range falls between 0.1 and 10. Anyone working in field units will recognise the same expression written as J = 0.2165 × Pc[psi] / (σ[dyne/cm]·cos θ) × √(k[mD]/φ).
The J-function delivers what it promises only inside one rock-type: collapsing clean sandstone curves together with vuggy carbonate curves builds no master curve, just a second cloud. The square root of k/φ stands as a crude proxy for pore throat radius, and it breaks down precisely where the throat size distribution turns bimodal. Contact angle has to stay under 90°: past that the cosine flips sign, the system reads oil-wet, the normalisation loses meaning, and the page refuses to calculate. Porosity goes in as a fraction, never a percentage — typing 22 instead of 0.22 triggers the same rejection, which at least makes the slip visible on the spot.
Frequently asked questions
Why does permeability go in as millidarcy when the formula wants m²?
Can I leave the contact angle at zero?
Does the tool build the full J curve against saturation?
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.